1. Field of the Invention
A power source monitor and method to monitor operating line conditions of an electrical power outlet.
2. Description of the Prior Art
Various types of metering equipment are available to measure power line sources. The classic multimeter comprising two probes with selectable functions and ranges is cumbersome and awkward to use. The probes are placed into high voltage power receptacles, moved from hole to hole and require knowledge of systematic measurement techniques to analyze power source connections. Other testing devices simply plug into the receptacle to read the voltage and still other devices simply to test the wiring. Popular plug-in analog voltmeters are inexpensive but lack accuracy. They are average reading only for use only with sine wave sources. The small plug-in wire diagnostics testers are effective only for analyzing wiring combinations only. These products require that the user have both types used in sequence or to use two outlets. Most do not have back lighting, limiting use to days only. Some newer meters are multifunction with voltage, wiring diagnostics and sometimes frequency. They use LED displays that are difficult to read in direct sunlight and use average voltage measurement for sine wave sources. Meters require RMS or Root Mean Square technology to measure non-sine wave sources accurately. Such meters measure, not monitor. These meters lack audible alarms to indicate fault conditions, requiring periodic reading.
The original Digital Line Monitor Model 662 test device provided rectified average voltage measuring shown on an LED display along with wire diagnostics and surge protection. When introduced, Graphic Line Monitor Model 8040 included a color-coded bar graph display, wire diagnostics and surge protection.
Most meters on the market use rectified average voltage measurement and do not work on modified sine or square wave sources such as solid state generators, inverters and Uninterruptible Power Supplies (UPS) with useful accurately. The RMS voltage measurement technique is the only method for accurately measuring power sources. The RMS measurement value of a voltage source refers to power delivering capability or effective value. The RMS value is equal to the value of a DC source, which would deliver the same power if it were, replaced a time-varying AC source. For example if an rectified average measuring meter is used to measure a modified sine wave source at full duty cycle it will display a 29% error in its voltage reading. The cost of the RMS measuring equipment has been traditionally much more costly than average measuring devices, therefore only usually available in expensive digital multi-meters.
U.S. Pat. No. 5,144,232 discloses an example of testing devices typical of such instruments used to monitor various line conditions.